Method for scavenging mercury

ABSTRACT

Disclosed herein is a method for removing mercury from a gas stream comprising contacting the gas stream with a getter composition comprising bromine, bromochloride, sulphur bromide, sulphur dichloride or sulphur monochloride and mixtures thereof. In one preferred embodiment the getter composition is adsorbed onto a sorbent. The sorbent may be selected from the group consisting of flyash, limestone, lime, calcium sulphate, calcium sulfite, activated carbon, charcoal, silicate, alumina and mixtures thereof. Preferred is flyash, activated carbon and silica.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.12/355,151, filed Jan. 16, 2009, now U.S. Pat. No. 7,754,170, which is acontinuation application of U.S. Ser. No. 11/101,713 filed Apr. 7, 2005,now U.S. Pat. No. 7,479,263, which claims priority to U.S. ProvisionalPatent Application 60/560,904 filed on Apr. 9, 2004, each of which isincorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENTAL SUPPORT

This invention was made during work supported by U.S. Department ofEnergy under Contract No. DE-AC03-76SF00098. The government has certainrights in this invention.

BACKGROUND OF THE INVENTION

The U.S. Environmental Protection Agency (EPA) has estimated that annualemissions of mercury from human activities in the United States were 158tons during the period of 1994-1995. Approximately 87% of theseemissions were from combustion sources. Coal-fired power plants in theU.S. were estimated to emit 48 tons of mercury per year into the airduring this period, or about one-third of anthropogenic emissions. Themercury in the flue gas from the power plants has been found in avariety of chemical forms, including elemental mercury and oxidizedmercury compounds. A study performed by Electric Power ResearchInstitute (EPRI) indicated that approximately 40% of the mercuryemissions from coal-fired power plants were in the oxidized form. Theoxidized mercury compounds, such as mercuric chloride, are water solubleand can be removed in a wet scrubber system. However, elemental mercuryis not water soluble and easily escapes the wet scrubber.

In addition to the difference in solubility, elemental mercury hashigher vapor pressure than the oxidized mercury. Consequently, elementalmercury does not adsorb on sorbents or unburned carbon as readily asoxidized mercury.

Mercury causes environmental and ecological problems. Elemental mercurycan be transported over long distance in the atmosphere because of itsinsolubility, whereas oxidized mercury deposited near the point ofemission as a result of its dissolution in fog, cloud, or rain. Once themercury has deposited on land or water, it can transform into methylmercury, an organic form, and thereby enter the food chain. Humans aremost likely to be exposed to methyl mercury through consumption of fish.

Specific technologies for the control of mercury such as wasteincinerators are already proving successful. However, these controlscannot be transposed to coal-fired power plants as the flue gasconditions are different. Flue gas streams from coal-fired power plantsare much larger than those from incinerators and the mercuryconcentrations are much lower, 0.01 ppm in coal-fired plants, at leastan order of magnitude lower than incinerator flue gases. Also, theresidence time of the flue gases in the air pollution control systems ofwaste incinerators is longer.

The injection of a sorbent such as activated carbon appears to be one ofthe most favorable options for mercury control. The sorbent would beinjected upstream of existing particulate control devices such as ESP orbaghouses. Mercury capture by an injected sorbent depends on the sorbentcapacity and mass transfer to the sorbent surface. The capacity andreactivity are affected by temperature and mercury concentration.However, the addition of a sorbent would obviously increase theparticulate load in an ESP or baghouse. The total cost of usingactivated carbon is estimated to add 24$/kW to the plant capital costand would increase the cost of electricity in the USA by 23%.

Gadkaree et al. U.S. Pat. No. 6,258,334 claimed a method of making andusing an activated carbon having sulfur chemically bonded to removemercury from fluid stream.

Madden et al. U.S. Pat. No. 6,372,187 used an alkaline sorbent injectionfor mercury control. Alkaline sorbents at low stoichiometric molarratios of alkaline earth or alkali metal to sulfur of less than 1.0 areinjected into a power plant system to remove at least between about 40%and 60% of the mercury content from combustion flue gases.

Felsvang et al. U.S. Pat. No. 5,435,980 patented a method for theremoval of mercury from flue gas of coal-fired power plants by adding achloride or chlorine containing material to the coal before of duringthe combustion or by injecting gaseous HCl into the flue gas upstreambefore a spray drying system.

Mendelsohn et al. U.S. Pat. No. 5,900,042 claimed the use of anoxidizing solution to convert elemental mercury to soluble mercurycompounds. The aqueous oxidizing solution claimed includes aqueousiodine solution, aqueous bromine solution, aqueous chlorine solution,aqueous chloric acid solution, and combination therefore. This solutionis impractical because of the aqueous nature of the oxidizing solution.The oxidant will hydrolyze to form acidic compounds that are notselective for Hg oxidation.

Dangtran et al. U.S. Pat. No. 6,375,909 patented a process of injectingcalcium chloride into the combustor and lowering the flue gastemperature in sufficient time to enhance oxidation of mercury andnitrogen oxides into more soluble products prior to their absorption ina wet scrubber.

On Mar. 15, 2005 the EPA promulgated new mercury regulations requiringcoal burning power plants to decrease the mercury emissions from theestimated 48 tons a year to 31.3 tons in 2010, 27.9 tons in 2015 and24.3 tons in 2020. These numbers correspond to a reduction from thecurrent emission levels of 34.8, 41.9 and 49.4 in 2010, 2015 and 2020respectively.

Cost will be a very important factor in deciding which of the manymercury control options currently under development is chosen forcommercialization. Most estimates of the cost of the impending mercurycontrol in the USA assume that activated carbon will be the controlmethod of choice. For a 45% control level, the US DOE has estimated thatthe annual costs would be between $1.08 and $3.02 billion per year(based on costs for activated carbon). This is based on a cost of25,000-70,000 $/lb (11,300-31,800 $/kg) of mercury removed.

To solve the aforementioned problems the present invention provides amethod using a getter composition that oxidizes volatile and/orinsoluble Hg to non-volatile and/or soluble Hg compounds that are thenreadily removed from gas streams.

BRIEF SUMMARY OF THE INVENTION

In one embodiment the present invention discloses a method for removingmercury from a gas stream comprising contacting the gas stream with agetter composition comprising bromine, bromochloride, sulphur bromide,sulphur dichloride or sulphur monochloride and mixtures thereof. In onepreferred embodiment the getter composition is adsorbed onto a sorbent.The sorbent may be selected from the group consisting of flyash,limestone, lime, calcium sulphate, calcium sulfite, activated carbon,charcoal, silicate, alumina and mixtures thereof. Preferred is flyash,activated carbon and silicate. Especially preferred is activated carbon.The adsorbed sorbent is collected in a baghouse or electrostaticprecipitator.

In another embodiment the getter composition is in a gaseous state. Thegetter composition may be introduced as a liquid and allowed to orforced to vaporize prior to contact with Hg.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 represents the oxidation of mercury vapor by bromochloride gaswith reaction time.

FIG. 2 represents the oxidation of mercury vapor by sulfur dichloridegas with reaction time.

FIG. 3 represents the effect of H₂O, NO, CO, or SO₂ gas on the oxidationof mercury by sulfur dichloride gas as a function of time.

FIG. 4 shows the time dependent oxidation of mercury gas by sulfurmonochloride and sulfur dichloride on flyash surface.

FIG. 5 shows the time dependent oxidation of mercury gas by sulfurmonochloride and sulfur dichloride on activated carbon.

FIG. 6 shows the oxidation of 50% mercury by adsorbed sulphurmonochloride, (S₂Cl₂) and sulphur dichloride (SCl₂) on activated carbonas a function of temperature.

FIG. 7 shows the time needed to oxidize 50% (half life, t_(1/2)) ofmercury gas on flyash bearing sulfur monochloride or sulfur dichlorideas a function of temperature.

FIG. 8 shows the effect of waste gas components on the half-life(t_(1/2)) of mercury gas, Hg⁰, oxidation on fly ash and activated carbonbearing sulfur dichloride.

FIG. 9 shows the effect of waste gas components on the half-life of Hg⁰,oxidation on fly ash and activated carbon bearing sulfur monochloride.

FIG. 10 the fraction of Hg⁰ oxidized by Br₂ in a simulated flue gas,containing 3000 ppm SO₂, 200 ppm NO, 40 ppm CO, and 45 ppm H₂O. Theinitial concentration of Br₂ and Hg⁰ was 17 ppm and 1.8 ppm,respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By “removing mercury” it is meant that at least some of any mercurypresent in a gas stream be oxidized by the getter compositions andmethods described herein.

By “gas stream” it is meant any volume of material that at leastpartially comprises a gas with at least some amount of mercury therein.This includes industrial gas streams such as flue gases in coal firedpower plants.

By “contacting the gas stream” it is meant the process of delivering thegetter composition to the elemental mercury. Processes are known in theart for this. The invention contemplates that this includes the processof delivering solid sorbent materials to the gas stream containing Hg.This may include providing sorbent from a hopper to a screw feeder thanto a pneumatic feed line which is supplied by a blower or compressorwhich will enable the sorbent to be delivered to the gas stream in aneffective amount. The sorbent may also be distributed by feeders whichare known in the art. The invention contemplates the use of a drysorbent feeder, a sorbent slurry feeder, sorbent filter cake feeder, anda feeder system. The invention also contemplates the use of a gas-solidreaction unit for reacting the mercury in the gas stream with the gettercomposition and may be selected from the group including, but notlimited to, a fluidized bed, a pseudo-fluidized bed, a reaction column,a fixed bed, a pipe/duct reactor, a moving bed, a serpentine reactor, acyclone, a multiclone, or combinations thereof.

By “getter composition” it is meant a composition comprising bromine,bromochloride, sulphur bromide, sulphur dichloride or sulphurmonochloride and mixtures thereof. It is understood that the gettercomposition may be in a gas state, may be in a liquid state andvaporized prior to contacting the Hg, and may be adsorbed onto asorbent. Sometimes the getter composition is referred to as an oxidantor scavenger.

By “effective amount” it is meant that quantity of getter compositionthat will scavenge a desired portion of Hg. The amount that is “desired”will of course depend on conditions and may be high in some instancesand low in other circumstances.

By “sorbent” it is meant a material onto which the getter compositionmay be adsorbed. These materials are known in the art and non limitingexamples include flyash, limestone, lime, calcium sulphate, calciumsulfite, activated carbon, charcoal, silicate, alumina and mixturesthereof. Preferred is activated carbon. The sorbent is preferably usedin finely divided form, preferably having an average particle diameterin the range of from about 1-100 microns, with 10-70 microns beingpreferred and 20-40 microns being especially preferred. The sorbent maybe in the form of pellets or a monolithic body. The sorbent may beflakes, or platelets or fibers. In one preferred embodiment the sorbentis a polymeric material that is functionalized to assist in theadsorption of the getter composition. Metal oxides such as disclosed inUS Published patent application 20040109800, the contents of which arehereby incorporated by reference in its entirety are also contemplated.The amount of getter composition adsorbed onto the sorbent may varydepending on the desired end use, the use of catalysts such as flyash.Optimization of the amount of getter composition to use may be readilydetermined by one having ordinary skill in the art. Sorbent coatingmethods are known in the art and the coating of the sorbent used hereinis not within the scope of this invention.

By “adsorbed onto a sorbent” it is meant that association between thesorbent and molecule that is normally associated with this structure inthe art.

By “liquid” it is meant to include a non-aqueous material not in thesolid or gas phase having at least a liquid component comprising atleast bromine, bromochloride, sulphur bromide, sulphur dichloride orsulphur monochloride and/or mixtures thereof. This may be a solution, amixture or a colloidal suspension, depending on solubility parametersthat one of skill in the art will recognize. Liquid water is detrimentalto the reaction chemistry and is not desired. However, water vapor maybe tolerated.

By “distributing a liquid” it is meant the process of delivering aliquid by pumping, spraying or other means known in the art such thatthe liquid will substantially vaporize just prior to contact with themercury. One skilled in the art will appreciate that this will includefluid nozzles, pressurized nozzles, ultrasonic nozzles, a rotaryatomizer or combinations thereof. In one non-limiting embodiment thenozzle will spray a mist of getter composition into the gas stream (fluegas, for example) so that the elemental mercury is oxidized into asoluble mercuric compound.

A halogen containing oxidant, including bromine, bromochloride, sulfurbromide, sulfur dichloride, and/or sulfur monochloride, in gas or liquidform, is injected into a waste gas stream to oxidize elemental mercuryvapor. In one embodiment of the present invention the oxidation takesplace in gas phase. In another embodiment the oxidation may take placeon flyash in an electrostatic precipitator or baghouse. The oxidizedform of mercury can subsequently be removed by the dissolution in anaqueous gas absorber or by the adsorption on sorbents in a baghouse orelectrostatic precipitator. The excess oxidant can react with water andbe captured by a wet SO₂ scrubber or ESP/baghouse located downstreamfrom the injection point. This new method can be used to control mercuryemissions from coal-fired power plants in a simple and cost effectivemanner.

A method has been discovered for removing elemental mercury from wastegas streams. This method involves the injection of a halogen containingoxidant, including bromine, bromochloride, sulfur bromide, sulfurdichloride, and/or sulfur monochloride, in gas or liquid form, intowaste gas to oxidize the elemental mercury to mercuric and/or mercurouscompounds. The mercuric and/or mercurous compounds are water soluble andcan be removed in an aqueous scrubber. Also, the mercuric/mercurouscompounds are much less volatile than the elemental mercury and can beremoved in a baghouse or an ESP by the adsorption on sorbent. Thismethod is effective for the oxidation of mercury in flue gas alsocontaining CO, NO and/or SO₂ because of its selectivity in oxidizingelemental mercury vapor over the CO, NO and/or SO₂.

In a preferred embodiment of the present invention sulphur dichloride isadded in the gas phase. One unexpected advantage of this invention isthat the product of the chemistry may be a stable insoluble mercurysulfide. This advantageous results means that upon disposal into solidwaste streams, the mercury sulfide will not leach back into theenvironment.

In a preferred embodiment of the present invention sulphur monochlorideis adsorbed onto a sorbent. One unexpected advantage of this inventionis that the product of the chemistry may be a stable insoluble mercurysulfide. This advantageous results means that upon disposal into solidwaste streams, the mercury sulfide will not leach back into theenvironment.

The sulfur chlorides used by the present invention may be prepared byany method known in the art. Non limiting prior art methods aredisclosed in Ding W., Xiao C. L., Li B. L., Zhang, R. M., Lu C. X.One-step Synthesis of Sulfur chloride Using Sulfur and Chlorine, FineChemicals, 16, 60-62, 1999 and Rosser, R. J., Whitt, F. R. Developmentof a Large-Scale Distillation and Process for Purifying Crude SulfurDichloride. J. Appl. Chem., 10, 229-237, 1960, the contents of which areboth incorporated by reference in their entirety.

In one embodiment it is preferable to use bromine in the gaseous form.

It is understood that the present invention contemplates wet scrubbingtechniques for further mercury removal in addition to contacting the gasstream with getter compositions as described herein. For example,subsequent to oxidization of Hg to soluble mercuric compounds by gettercompositions, the treated gas stream may travel to a wet scrubber. Inthe wet scrubber the soluble mercuric compounds and other constituentsare treated with aqueous solutions and/or slurry of calcium carbonate,sodium carbonate, magnesium carbonate and sodium hydroxide to remove thesoluble compounds. Treated flue gas may then be vented from the wetscrubber.

The present invention contemplates that other wet flue gasdesulphurization systems such as flue gas desulphurization spray dryersor a wet electrostatic precipitator (ESP) may be used in combinationwith the present method and getter composition.

EXAMPLE 1 Mercury Scavenging Using Bromochloride

Mercury gas was mixed with bromochloride gas in a reactor. The decay ofthe mercury gas concentration as a function of reaction time wasmonitored by cold vapor atomic absorption spectroscopy. In thisnon-limiting embodiment the mercury gas and gas oxidants were introducedinto the reactor by injection with a syringe. Initially, the reactor wasevacuated nitrogen gas saturated with mercury gas was injected with asyringe to the reactor to reach a pressure of about 250 torr. Thepressure in the reactor is raised to 500 torr with nitrogen. A volume ofknown concentration of bromochloride gas in nitrogen was injected by asyringe into the reactor before the pressure was quickly brought to 760torr (1 atm) with nitrogen. The initial bromochloride gas concentrationsstudied were 6.4 ppm, 12.8 ppm, and 18.1 ppm. The initial mercuryconcentrations were 0.18 ppm in all experiments. The half life (50%conversion) of mercury vapor was measured to be 14 sec with 6.4 ppmbromochloride gas, 8.5 sec with 12.8 ppm of bromochloride gas, and 6.5sec with 18.1 ppm of bromochloride. The results are shown in FIG. 1.

EXAMPLE 2 Mercury Scavenging Using Sulfur Dichloride

Mercury gas was mixed with sulfur dichloride gas in a reactor. The decayof the mercury gas concentration as a function of reaction time wasmonitored by cold vapor atomic absorption spectroscopy. In thisembodiment, the mercury gas and sulfur dichloride gas were introducedinto the reactor by injection with a syringe. A volume of nitrogen gassaturated with mercury gas was injected with a syringe to reach apressure of about 250 torr. The pressure in the reactor was raised to500 torr with nitrogen. A volume of known concentration of sulfurdichloride gas in nitrogen was injected by a syringe into the reactorbefore the pressure was quickly brought to 760 torr (1 atm) withnitrogen. The initial sulfur dichloride gas concentrations studied were15 ppm, 43 ppm, and 86 ppm. The initial mercury concentrations were 0.18ppm in all experiments. The half life (50% oxidation) of mercury vaporwas measured to be 14 sec with 15 ppm sulfur dichloride gas, 5 sec with43 ppm of sulfur dichloride gas, and 4 sec with 86 ppm of sulfurdichloride gas. FIG. 2 shows the results.

EXAMPLE 3 Simulation of Waste Gas Components on the Scavenging ofMercury

To demonstrate the effect of different waste gas components (H₂O, NO,CO, and SO₂) on the oxidation rate of mercury vapor by sulfur dichlorideas a function of time at 24° C. experiments were performed mixingmercury gas with sulfur dichloride gas in the presence of differentwaste gas components in a reactor. The decay of the mercury gasconcentration as a function of reaction time was monitored by cold vaporatomic absorption spectroscopy. The mercury gas, sulfur dichloride gas,and waste gas component were introduced into the reactor by injectionwith a syringe. The initial concentrations of mercury gas, sulfurdichloride, water vapor (H₂O), nitric oxide (NO), carbon monoxide (CO),and sulfur dioxide (SO₂) were 0.18 ppm, 15 ppm, 0.14%, 780 ppm, 300 ppm,and 1500 ppm, respectively. All waste gas components studied didn'texhibit a significant decrease in the oxidation rate of mercury. FIG. 3shows the results.

EXAMPLE 4 Oxidation of Mercury by Sulfur Monochloride (S₂Cl₂) and SulfurDichloride (SCl₂)

To make the getter composition, flyash was coated with sulfurmonochloride and sulfur dichloride at 296±1° K. and 1 atm. The flyash(size: 20-40 μm) was dispersed on the inner wall of a reactor using ahalocarbon wax. The amount of fly ash used was 1.34 g. The weightpercentages of S₂Cl₂ on flyash were 0.0013% and 0.0035% for 8 ppm and 22ppm of S₂Cl₂, respectively. The weight percentages of SCl₂ on flyashwere 0.0010% and 0.0026% for 8.4 ppm and 24 ppm of SCl₂, respectively.The initial concentration of mercury gas, [Hg⁰]₀, in the reactor was 0.2ppm. FIG. 4 shows the results.

EXAMPLE 5 Oxidation of Mercury Gas by Sulfur Monochloride and SulfurDichloride on Activated Carbon at 296±1° K. and 1 Atm

The activated carbon (size: 20-40 μm) was coated on the inner wall of areactor. The amount of activated carbon employed was 0.36 g. Theactivated carbon was then exposed to adsorb oxidants. The weightpercentages of (S₂Cl₂) on activated carbon were 0.0048% and 0.012% for 8ppm and 22 ppm of (S₂Cl₂), respectively. The weight percentages of(S₂Cl₂) on activated carbon were 0.0037% and 0.0093% for 8.4 ppm and 24ppm of (S₂Cl₂), respectively. The initial concentration of mercury gas,[Hg⁰]₀ in the reactor was 0.2 ppm. FIG. 5 shows the results.

EXAMPLE 6 Oxidation of Mercury on with Adsorbed S₂Cl₂ on ActivatedCarbon as a Function of Temperature

The initial concentration of Hg⁰ in the reactor was 0.2 ppm. Theactivated carbon (size: 20-40 μm) bearing sulfur chlorides was coated onthe inner wall of a reactor using a halocarbon wax. The amount ofactivated carbon used was 0.36 g. The weight percentage of (SCl)₂ onactivated carbon was 0.012% for 22 ppm of (SCl)₂. The weight percentageof SCl₂ on activated carbon was 0.0093% for 24 ppm of SCl₂. FIG. 6 showsthe results.

EXAMPLE 7 The Time Needed to Oxidize 50% (Half Life, t_(1/2)) of MercuryGas on Flyash Bearing Sulfur Monochloride or Sulfur Dichloride as aFunction of Temperature

The initial concentration of mercury gas, Hg⁰, in the reactor was 0.2ppm. The flyash (size: 20-40 μm) was coated on the inner wall of areactor using a halocarbon wax. The amount of flyash used was 1.34 g.The weight percentage of S₂Cl₂ on flyash was 0.0035% for 22 ppm ofS₂Cl₂. The weight percentage of S₂Cl₂ on flyash was 0.0026% for 24 ppmof S₂Cl₂. FIG. 7 shows the results.

EXAMPLE 8 The Effect of Waste Gas Components on the Half-Life (t_(1/2))of Mercury Gas, Hg⁰, Oxidation on Fly Ash and Activated Carbon BearingSulfur Dichloride at 296° K. and 358° K. were Studied

Waste gas conditions studied include NO (100 ppm), H₂O (1.2% volume),and a simulated flue gas, Mix (1200 ppm SO₂+120 ppm CO+100 ppm NO+1.2%H₂O+7% O₂+N₂ the balance). Fly ash or activated carbon (20-40 μm) wascoated on the inner surface of a reactor using a halocarbon wax. Theamount of fly ash and activated carbon was 0.36 g and 1.34 g,respectively. The concentration of SCl₂ was 24 ppm, and the percentagesof SCl₂ on fly ash and activated carbon was 0.0026% and 0.0093%,respectively. The initial concentration of mercury gas, Hg⁰, in thereactor was about 0.2 ppm. The results are shown in FIG. 8.

EXAMPLE 9 The Effect of Waste Gas Components on the Half-Life of Hg⁰Oxidation on Fly Ash and Activated Carbon Bearing Sulfur Monochloride at296° K. and 358° K.

Waste gas conditions studied include NO (100 ppm), H₂O (1.2% volume),and a simulated flue gas, Mix (1200 ppm SO₂+120 ppm CO+100 ppm NO+1.2%H₂O+7% O₂+N₂ the balance). Fly ash or activated carbon (20-40 μm) wascoated on the inner surface of a reactor using a halocarbon wax. Theamount of fly ash and activated carbon was 0.36 g and 1.34 g,respectively. The concentration of (SCl)₂ was 22 ppm, and thepercentages of (SCl)₂ on fly ash and activated carbon was 0.0035% and0.012%, respectively. The initial concentration of Hg⁰ in the reactorwas about 0.2 ppm. The results are shown in FIG. 9.

EXAMPLE 10 Oxidation of Hg Using Bromine

The initial mercury vapor and bromine gas were 1.8 and 17 ppm,respectively. The concentration of the simulated flue gas compositionwas 3000 ppm SO₂, 200 NO, 40 ppm CO and 45 ppm H₂O. The results shown inFIG. 10 show that the fraction of mercury oxidized increases withincreased temperature. The fraction of mercury oxidized was 77% and 92%at 21° C. and 50° C. respectively after 10 seconds of reaction time. Thefigure also shows that the net effect of a gas mixture containing SO₂,NO, H₂O, and CO was an enhancement of mercury oxidation rate by brominegas.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding equivalents of thefeatures shown and described, or portions thereof, it being recognizedthat various modifications are possible within the scope of theinvention claimed. Moreover, any one or more features of any embodimentof the invention may be combined with any one or more other features ofany other embodiment of the invention, without departing from the scopeof the invention.

All patents, patent applications, and publications mentioned above areherein incorporated by reference in their entirety for all purposes.None of the patents, patent applications, and publications mentionedabove are admitted to be prior art.

1. A method for removing mercury from a gas stream, comprisingcontacting the gas stream with a getter composition that oxidizesvolatile or insoluble Hg to non-volatile or soluble Hg, wherein saidgetter composition comprises bromine, bromochloride, sulphur bromide,sulphur dichloride or sulphur monochloride and mixtures thereof, furthercomprises processing the gas stream treated with the getter compositionin a wet scrubber, where the soluble Hg and other constituents of thegas stream are treated with aqueous solutions or slurries of calciumcarbonate, sodium carbonate, magnesium carbonate and sodium hydroxide toremove the soluble Hg.
 2. A method according to claim 1, furthercomprises venting the gas stream processed in the wet scrubber.
 3. Amethod according to claim 1, wherein the getter composition isbromochloride.
 4. A method according to claim 1, wherein the gettercomposition is sulphur bromide.
 5. A method according to claim 1,wherein the getter composition is sulphur dichloride or sulphurmonochloride.
 6. A method for removing mercury from a gas stream,comprising: contacting the gas stream with a getter composition thatoxidizes volatile or insoluble mercury to non-volatile or solublemercury, wherein the getter composition comprises bromine,bromochloride, sulphur bromide, sulphur dichloride, or sulphurmonochloride and mixtures thereof and said getter composition isadsorbed onto a sorbent, wherein the sorbent is selected from the groupconsisting of limestone, lime, calcium sulfate, calcium sulfite,silicate, alumina, silica, activated carbon and mixtures thereof.
 7. Amethod according to claim 6, further comprises processing the gas streamtreated with the getter composition in a wet scrubber, where the solubleHg and other constituents of the gas stream are treated with aqueoussolutions or slurries of calcium carbonate, sodium carbonate, magnesiumcarbonate and sodium hydroxide to remove the soluble Hg.
 8. A methodaccording to claim 7, further comprises venting the gas stream processedin the wet scrubber.
 9. A method according to claim 6, wherein thesorbent is activated carbon.
 10. A method for removing mercury from agas stream, comprising: contacting the gas stream with a gettercomposition that oxidizes volatile or insoluble mercury to non-volatileor soluble mercury, wherein the getter composition comprises bromine,bromochloride, sulphur bromide, sulphur dichloride, or sulphurmonochloride and mixtures thereof and said getter composition isadsorbed onto a sorbent, and wherein the sorbent is selected from thegroup consisting of carbonaceous materials, flyash and mixture thereof,further comprises processing the gas stream treated with the gettercomposition in a wet scrubber, where the soluble Hg and otherconstituents of the gas stream are treated with aqueous solutions orslurries of calcium carbonate, sodium carbonate, magnesium carbonate andsodium hydroxide to remove the soluble Hg.
 11. A method according toclaim 10, further comprises venting the gas stream processed in the wetscrubber.